The present invention relates, in general, to a parking brake assembly for a railway vehicle braking system and, more particularly, to a spring applied parking brake assembly for a railroad vehicle braking system which is activated by the absence of air in the railway vehicle braking system. The spring applied parking brake assembly of the invention is applicable to both truck and car mounted brake assemblies.
As is generally well known in the railway industry, when railway cars are taken out of a train and parked at a siding or yard, the hand brake or parking brake on at least some of these cars is applied as a precaution against unwanted or unexpected movement of the cars. A typical railway car hand brake system normally consists of an apparatus for manually applying and biasing one or more brake shoes against the tread of one or more wheels of the railway car by either turning a hand wheel or pumping a ratchet handle on a hand brake mechanism attached to the railway car.
As illustrated in FIG. 4, in truck mounted braking systems, the hand brake mechanism is usually either a cast or stamped metal gear housing usually attached to an outside end wall of the railway car and having a rotatable chain drum therein which can be rotated by turning the hand wheel to wind a brake chain onto the chain drum. The other end of the brake chain normally extends through the bottom of the gear housing and is interconnected with cable or other linkage, such as a hand brake lever, to the brake beam which carries the brake shoes such that winding of the brake chain onto the chain drum will apply tension to the brake chain and linkage as necessary to draw the interconnected brake shoes against the tread surfaces of adjacent railway car wheels and, accordingly, apply the hand brake as intended.
A disadvantage of this prior art type hand brake arrangement is that an operator must manually apply the parking brake to each car which requires a considerable amount of time and labor. Additionally, the operator must be certain that the handwheel is turned a sufficient amount to ensure that the parking brake is engaged. Also, the possibility exists that the operator may forget to apply the brake altogether, which could result in unexpected movement of the car while parked at the siding or yard. Furthermore, operation of the handwheel requires exerting a considerable amount of physical force from an awkward position. This, in turn, makes the hand brake difficult to apply.
Briefly, the invention comprises a cylindrical casing which is engaged with a railroad vehicle braking system. A piston assembly, including a piston and a piston rod, is provided within the cylindrical casing. This piston assembly is mounted for longitudinal movement within the casing upon the application and/or removal of pneumatic pressure to the piston assembly. An attachment means is disposed on the piston rod for associating the piston assembly with the non-cylinder force transfer lever of the braking system so as to apply a force to this non-cylinder force transfer lever upon longitudinal movement of the piston assembly. At least one spring member, preferably two spring members, are provided within the cylindrical casing. These spring members have a first end which abuts against an end wall of the cylindrical casing and a second end which contacts the piston and applies a force to the piston assembly to achieve longitudinal movement of the piston assembly upon removal of pneumatic pressure to the braking system and the piston assembly. This constantly applied force from the spring members causes the piston assembly to retract within the casing and the force transfer lever to rotate in a counterclockwise direction to cause an application of the brakes to the braking system. Thus, once the train is removed from the train consist and the air supply for the pneumatic braking system has been disconnected, the brakes of the train are automatically applied.
At least one opening is provided within the cylindrical casing to enable the application of pneumatic pressure to the piston assembly to cause this piston assembly to move in a longitudinal direction to compress the springs and to drive the piston rod out of the cylindrical casing to cause the non-cylinder force transfer lever to rotate in a counterclockwise direction to cause a release of the brakes.
The spring applied parking brake of the invention also includes a manual quick release system which allows the parking brake to be released during shunting operations or anytime that it is desirable to move the vehicle when no air is present. This manual quick release system comprises a half moon shaped cam operating in a xe2x80x9ckeyholexe2x80x9d shaped slot. The half moon cam lies crosswise in the circular end of the keyhole during normal operations. A handle attached to the cam is manually operated to effect a quick release by rotating the cam so that the cam aligns with the elongated portion of the keyhole shaped slot. The force of the springs within the spring applied parking brake draws the cam into the slot in a first direction to effectively release the force applied by the spring applied parking brake on the non-cylinder force transfer lever and consequently causes a release of the parking brake.
The spring applied parking brake will remain in a released position, with the quick release handle pulled out, until a normal air pressure actuated brake release is make. When this occurs, the piston and rod assembly will move to compress the springs and move the cam forward, or in a second direction, in the slot. As the cam enters the circular end of the keyhole, a torsion spring on the cam shaft will rotate the cam so that it again lies crosswise in the keyhole. As this occurs the handle rotates clockwise and impacts a striker plate attached to the front of the parking brake unit. The spring applied parking brake is now reset for normal operation.
It is an object of the present invention to provide a spring applied parking brake assembly for a railway vehicle braking system which is an ergonomic alternative to the currently used manually activated hand brake assemblies.
Another object of the present invention is to provide a spring applied parking brake assembly for a railway vehicle braking system which is particularly applicable to TMX(copyright) truck mounted braking systems (TMX(copyright) is a registered trademark to Westinghouse Airbrake Company, the assignee of the present invention).
Still another object of the present invention is to provide a spring applied parking brake assembly for a railway vehicle braking system which may be used to replace the currently used manually activated handwheel hand brakes.
A further object of the present invention is to provide a spring applied parking brake assembly for a railway vehicle braking system which is activated by the absence of air in the braking system ensuring that the parking brake is activated as soon as the car has been removed from the air braking system of the train thus providing a significant reduction in time and labor.
Yet another object of the present invention is to provide a spring applied parking brake assembly for a railway vehicle braking system which is automatically activated upon the removal of the car from the air braking system of the train, eliminating the possibility of operator error and/or injury during application of the parking brake.
An additional object of the present invention is to provide a manual quick release lever arrangement to enable a quick release of the spring applied parking brake of the invention during shunting operations or anytime it is desirous to move the vehicle when in the absence of air from the pneumatic braking system.
Although a number of objects and advantages of the present invention have been described in some detail above, various additional objects and advantages of the spring applied parking brake assembly of the present invention will become more readily apparent to those persons who are skilled in the art from the following more detailed description of the invention, particularly, when such detailed description of the invention is taken in conjunction with both the attached drawing figures and with the appended claims.